The present invention relates to a shaft for use in a machine to perform at least one operation. In particular, it relates to a light weight, low cost, compliant composite shaft assembly having a hollow, tubular, shell like portion with a helical pattern cut through along the axis and containing a hardened, moldable material within its core in communication with at least one molded feature on the outside of the helical pattern which may be at the end of the tubular shell like portion.
While the present invention has utility in apparatus comprising various mechanical components, it has particular application and will henceforth be described with reference to electrostatographic reproducing apparatus. Briefly, and as illustrated in FIGS. 1 and 2, in electrostatographic printing apparatus commonly in use today a photoconductive insulating surface 10 which is typically the surface of a rotatable drum is charged to a uniform potential by a charge corotron 12 and thereafter exposed to a light image of an original document 15 to be reproduced on an exposure platen 16 by means of exposure lamp 17, the exposure discharging the photoconductive insulating surface in exposed or background areas creating an electrostatic latent image on the photoconductive insulating surface of the document. A developer unit 20 is which corresponds to the image areas contained within the apparatus and has developer material to developed the electrostatic latent image. Typically, the developer material has charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles and during development, the toner particles are attracted from the carrier particles to the charged areas of the photoconductive insulating surface. The developed image on the photoconductive insulating layer is subsequently transferred at a transfer station 24 to a support surface, such as copy paper 21, which is fed by feeder 22 to provide intimate transfer contact between the insulating area and the copy paper. The toner image on the copy paper is subsequently, permanently affixed on the copy paper by the application of heat and/or pressure in a fuser 23. Subsequent to the transfer of the toner image to the support surface, any residual toner remaining on the photoconductor is cleaned in a cleaner 24 in preparation for the next imaging cycle. FIG. 2 illustrates the claim shell nature of this machine having a lower frame member 25 and an upper frame member 26 which has two shafts, 27, 28 in the copy sheet transport system.
Alternatively, the electrostatic latent image may be generated from information electronically stored or generated in digital form which afterwards may be converted to alphanumeric images by image generation, electronics and optics. For further information on such apparatus, attention is directed to U.S. Pat. No. 4,372,668 to Malachowski et al., and U.S. Pat. No. 4,660,963 to Stemmle et al.
In these machines, shafts are typically used to provide a variety of features performing functions within the machines. For example, shafts typically have gears, rolls, pulleys or other drive mechanisms mounted thereon to enable driving various parts or systems in the machine. In addition, the shafts may have retention or location features such as, snaps, fitting elements or stops or may contain other features such as bearings, bushings, rollers, journals and O-rings. Initially, the shafts were typically made from solid materials such as, metals like, steel and aluminum, and the individual functional features or elements such as rollers or gears were individually mounted to the shaft and secured thereto. Typically, this assembly process was manually completed as it did not readily lend itself to automated assembly. While satisfactory in many respects, such shaft assemblies were both heavy and costly in that solid shafts contained more metal and therefore cost more. Each of the individual functional features had to be separately manufactured, separately assembled onto the shaft assembly, all of which increased both materials and assembly time and cost particularly when most of the functional features had to also be located and fixed by way of set screws or other such device to the shaft. Alternatively, the functional features have been formed on metal stock material by such conventional metal working techniques as turning, milling and grinding. In addition, the weight of such shaft assemblies provided a high moment of inertia which necessitated increased drive power requirements.
Additional progress in terms of cost and weight of the shaft assemblies has been observed in certain machines which use hollow drive shafts with molded or otherwise separately fabricated functional features such as, gears and rolls which are then manually placed on the shaft and secured in position.
Another problem with shaft assemblies, and in particular, with shaft assemblies which have functional features such as pulleys, rolls, gears, etc., which may mate with another component and which is also present in the above referenced copending application, has to do with what is referred to in the art as runout, which is typically an eccentricity in the shaft itself or in a component mated to the shaft or both. Thus, for example, in a paper feeder wherein a sheet of paper is being fed through a nip formed between two rolls, one of which is driven, there is opportunity for eccentricity in both the shafts on which both rolls are mounted as well as the rolls themselves. Typical eccentricities are of the order of four to five-thousands of an inch per 12 inches of shaft length and if both shafts and both rolls have such an eccentricity it is entirely possible that the total runout of the sheet feeder could be as much as twenty-thousands of an inch. In such a feeder it is entirely possible that during the feeding operation one of the rolls in the feeder would lose contact with the paper being fed resulting in skewing of the sheet, mistracking and/or misfeeding. In order to overcome this problem and to keep the rolls in contact forming the sheet feeding nip to reliably feed sheets large, complex, expensive apparatus, including bearings, springs, etc., are typically used. Another example would be that of a fuser roll in an electrostatographic printing machine wherein the ends or centerline may be journaled perfectly but the fusing surface will not be a perfect circle around the circumference or along it's length.
To measure the runout the shaft assembly is placed in a V-block fixture wherein the ends of the shaft are journaled on the bearings surface and an indicator having a movable needle to follow the surface is placed on the functional surface such as a feed roll surface or a fuser roll. The functional surface is rotated and the concentricity of different portions of the circumference of the functional feature are observed. The total of what the indicator reads off of 0, the difference between the high and the low points on the indicator and therefore with respect to the concentricity are the runout, on the shaft assembly.